In general, to fabricate LEDs of blue, green, red and the like, it is required to first fabricate different substrates, such as InGaN substrate, GaN substrate, GaAs substrate, ZnO substrate. This requirement needs to use different semiconductor thin films, which causes the fabrication costs and unit price to be increased. Accordingly, if these LEDs can be fabricated using an identical semiconductor thin film, fabrication costs and investment costs can be remarkably reduced.
In the meanwhile, a white LED is gaining the popularity as the back light for the LCDs of a lighting device, a notebook computer, a handheld terminal and the like.
As a method for fabricating the white LED, there is a trial where a phosphor using a light emitted from an InGaN-based LED as the excitation energy source is further coated. For instance, the white LED is fabricated by coating a YAG:Ce (cerium) phosphor emitting a yellow light (wavelength: 560 nm) on a blue InGaN-based LED.
However, in emitting white light using the blue LED, besides the YAG:Ce or some organic luminescent materials, it is difficult to find out a proper phosphor excited by the blue LED.
In other words, the white LED using the blue LED is realized mainly using the YAG:Ce phosphor.
To solve the aforementioned drawbacks, it is strongly requested to introduce a new material capable of realizing yellow light instead of the YAG:Ce phosphor.